Septic System Installation in Hawaii

Hawaii Septic designs and installs septic systems and aerobic treatment units for new homes, ohana units, additions and cesspool replacements across the Hawaiian Islands. Our home base is Keaau on the Big Island, and our crews are built for the hard part of Hawaii septic work: lava rock, thin soil and tight lots.

New construction, additions and conversions

Most of our installs fall into three groups.

  • New homes. Hawaii has banned new cesspools since 2016, so every new house off the sewer needs an approved system from day one. The septic design affects where the house can sit and how many bedrooms it can have, so we like to get involved before your plans are final. Our new home septic guide covers the rules.
  • Additions and ohana units. Adding bedrooms usually means more septic capacity. One system can serve up to five bedrooms total, so a second dwelling sometimes needs its own system.
  • Cesspool replacements. A conversion is a septic install with the extra step of closing out the old cesspool. See our cesspool conversion page for how that works.

Systems we install

  • Conventional septic tank and leach field. The workhorse system where soil and space cooperate.
  • Seepage pits. For steep lots, very small lots, or sites where usable soil sits below a hard layer.
  • Aerobic treatment units. Higher treatment, useful where groundwater is shallow or setbacks are tight. ATUs must be certified models and need an active service contract with inspections every six months.
  • Soil replacement systems. Required on fractured lava. We excavate the rock and build the disposal area in suitable fill with at least three feet of separation above groundwater.
  • Mounds and other engineered designs. Reviewed by the Department of Health case by case for difficult sites.

Why lava rock is our specialty

Much of East Hawaii has only inches of soil over pahoehoe. A standard leach field won’t work there, and digging a tank hole can mean hours of breaking rock. That’s the work we’re set up for. Excavators, breakers and the right fill plan make the difference between a system that passes inspection the first time and one that drags on for weeks.

How we size a system

Hawaii’s rules size a home’s system by bedrooms, not by square footage. A few numbers that matter:

  • Design flow is 200 gallons per day per bedroom.
  • The minimum tank is 1,000 gallons for up to four bedrooms and 1,250 gallons for five.
  • Any room of 70 square feet or more is presumed to be a bedroom, so offices and dens can count.
  • Leach field size depends on how fast your soil absorbs water, which the engineer measures with a percolation test.

The install, start to finish

  1. We visit the lot and look at access, terrain and where the system can go.
  2. A Hawaii-registered engineer runs the soil profile and percolation test and designs the system.
  3. The design goes to the Department of Health for review. On new homes, DOH signs off on the wastewater system before the county building permit.
  4. We excavate, set the tank or treatment unit, build the disposal area and run the piping, bringing access lids up to grade for future service.
  5. The engineer inspects, photographs the work before backfill and files the final report.
  6. DOH issues the approval to use, and the system is ready.

Cost

Most installs land between $20,000 and $50,000. Rock, access, groundwater and advanced treatment push toward the top of that range. Our cost guide explains what drives the price, and we give itemized written estimates after a site visit.

Where we install

We install systems on every island. In East Hawaii, our Puna and Hilo pages break down conditions community by community, from catchment lots in Orchidland to young lava in Kalapana.

Have a lot or a project in mind? Request a free estimate.

Frequently Asked Questions

How big a septic tank does a house in Hawaii need?

At least 1,000 gallons for up to four bedrooms and 1,250 gallons for five. The engineer sizes the full system, including the leach field, from your bedroom count and soil test.

Can you install a septic system on solid lava?

Yes. On fractured lava, Hawaii’s rules require a soil replacement system, where we excavate the rock and build the disposal area in suitable fill. It takes more equipment and time, which is why these jobs cost more.

Do I need an engineer for a septic system in Hawaii?

Yes. A Hawaii-registered engineer has to design the system and submit it to the Department of Health. We coordinate that for you.

How long does a septic install take?

Design and DOH review take the longest, often several weeks combined. The installation itself is usually a matter of days, longer on rocky or hard-to-reach lots.

Should I get an aerobic treatment unit or a regular septic tank?

It depends on the site. A conventional tank is cheaper to buy and run. An ATU fits sites with shallow groundwater or tight setbacks, but it needs ongoing service. Your engineer’s soil data usually makes the choice clear.

Can I build an ohana on the same septic system?

Possibly. One system can serve up to five bedrooms total across both buildings. Beyond that, you’ll need a second system and enough land for it.